Plasma CVD method, method for forming silicon nitride film and method for manufacturing semiconductor device

ABSTRACT

A plasma processing apparatus generates plasma by introducing microwaves into a processing chamber by using a planar antenna having a plurality of slots. By using the plasma processing apparatus, a nitrogen containing gas and a silicon containing gas introduced into the processing chamber are brought into the plasma state, and at the time of depositing by using the plasma a silicon nitride film on the surface of the a substrate to be processed, stress to the silicon nitride film to be formed is controlled by the combination of the type and the processing pressure of the nitrogen containing gas.

FIELD OF THE INVENTION

The present invention relates to a plasma chemical vapor deposition(CVD) method, a method for forming a silicon nitride film using thesame, and a method for manufacturing a semiconductor device using thesame.

BACKGROUND OF THE INVENTION

A silicon nitride film is used as an insulating film, a protection filmor the like in various semiconductor devices. The silicon nitride filmmay be formed by a plasma CVD method using a silicon-containing gas suchas silane (SiH₄) and a nitrogen-containing gas such as nitrogen orammonia as source gases (see, e.g., Japanese Laid-open Publication No.2000-260767).

In the silicon nitride film formed by a conventional plasma CVD method,it is important to suppress stresses, i.e., tensile and compressivestresses, of the film, which have a bad influence on devicecharacteristics. For instance, if a compressive stress of the siliconnitride film is large, stress migration may occur to cause disconnectionof metal lines right under the film. Accordingly, the compressive stressneeds to be reduced to prevent such disconnection. In the plasma CVDmethod, the direction of stress (tensile stress or comprehensive stress)of the silicon nitride film or the magnitude of stress depends onprocess conditions including pressure, temperature, gas species, etc.Thus, conventionally, process conditions are set such that a strongstress is not applied to the silicon nitride film, and a silicon nitridefilm having no stress is formed by a plasma CVD method (e.g., MaetaGazuo ┌VLSI and CVD┘ Tenshoten, published on Jul. 31, 1997).

Recently, attempts have been made to take advantage of the stress ofsilicon nitride film to improve the device characteristics. However, forexample, a parallel plate type or inductively coupled plasma CVDapparatus utilizes plasma having a relatively high electron temperature.Accordingly, when film formation conditions such as high-frequencyoutput, pressure and temperature are changed to introduce a high stress,plasma damage may occur in the silicon nitride film. Thus, it isdifficult to obtain a high-quality silicon nitride film and it is alsodifficult to obtain a silicon nitride film having a high stress.Further, since there is a limitation in the plasma process conditions,it is also difficult to precisely control a stress.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a plasma CVD methodcapable of precisely controlling a stress of a silicon nitride filmformed by using a plasma CVD method and also reducing plasma damage.

Further, it is another object of the present invention to provide amethod for forming a silicon nitride film having a desired stress byusing the plasma CVD method.

Further, it is still another object of the present invention to providea method for manufacturing a semiconductor device using the siliconnitride film.

In accordance with a first aspect of the present invention, there isprovided plasma CVD method comprising: preparing a plasma processingapparatus including a vacuum evacuable processing chamber, a microwavegenerator for generating microwaves, a planar antenna having slots tointroduce the microwaves from the microwave generator into theprocessing chamber through the slots, and a gas supply system forsupplying a source gas for film formation into the processing chamber;loading a substrate to be processed in the processing chamber; andintroducing a nitrogen-containing gas and a silicon-containing gas intothe processing chamber, converting the gases into plasma with themicrowaves, and depositing a silicon nitride film on a surface of thesubstrate by using the plasma, wherein a stress of the silicon nitridefilm is controlled by selecting a type of the nitrogen-containing gasand a process pressure.

In the first aspect, when an ammonia gas is used as thenitrogen-containing gas, the silicon nitride film may be formed at aprocess pressure of 6.7 Pa or more to have a tensile stress of 400 MPaor more. Further, the silicon nitride film may be formed at a processpressure of 40 Pa or more to have a tensile stress of 800 MPa or more.Further, the silicon nitride film may be formed at a process pressure of133.3 Pa or more to have a tensile stress of 1500 MPa or more.

In the first aspect, when a nitrogen gas is used as thenitrogen-containing gas, the silicon nitride film may be formed at aprocess pressure less than 5.3 Pa to have a compressive stress of 800MPa or more. Further, the silicon nitride film may be formed at aprocess pressure of 4 Pa or less to have a compressive stress of 1000MPa or more.

In accordance with a second aspect of the present invention, there isprovided a method for forming a silicon nitride film, comprising:preparing a plasma processing apparatus including a vacuum evacuableprocessing chamber, a microwave generator for generating microwaves, aplanar antenna having slots to introduce the microwaves from themicrowave generator into the processing chamber through the slots, and agas supply system for supplying a source gas for film formation into theprocessing chamber; loading a substrate to be processed in theprocessing chamber; and introducing a nitrogen-containing gas and asilicon-containing gas into the processing chamber, converting the gasesinto plasma with the microwaves, and depositing a silicon nitride filmon a surface of the substrate by using the plasma, wherein an ammoniagas is used as the nitrogen-containing gas and the silicon nitride filmis formed at a process pressure of 6.7 Pa or more to have a tensilestress of 400 MPa or more.

In the second aspect, the silicon nitride film may be formed at aprocess pressure of 40 Pa or more to have a tensile stress of 800 MPa ormore, and at a process pressure of 133.3 Pa or more to have a tensilestress of 1500 MPa or more.

In accordance with a third aspect of the present invention, there isprovided a method for forming a silicon nitride film, comprising:preparing a plasma processing apparatus including a vacuum evacuableprocessing chamber, a microwave generator for generating microwaves, aplanar antenna having slots to introduce the microwaves from themicrowave generator into the processing chamber through the slots, and agas supply system for supplying a source gas for film formation into theprocessing chamber; loading a substrate to be processed in theprocessing chamber; and introducing a nitrogen-containing gas and asilicon-containing gas into the processing chamber, converting the gasesinto plasma with the microwaves, and depositing a silicon nitride filmon a surface of the substrate by using the plasma, wherein a nitrogengas is used as the nitrogen-containing gas and the silicon nitride filmis formed at a process pressure less than 5.3 Pa to have a compressivestress of 800 MPa or more.

In the third aspect, the silicon nitride film may be formed at a processpressure of 4 Pa or less to have a compressive stress of 1000 MPa ormore.

In the first to the third aspects, the silicon-containing gas may bedisilane (Si₂H₆). Further, the silicon nitride film may be deposited ata process temperature of 300° C. to 800° C.

In accordance with a fourth aspect of the present invention, there isprovided a method for manufacturing a semiconductor device, comprising:preparing a structure having a gate electrode formed on a main surfaceof a semiconductor substrate through an insulating film, and a sourceand a drain formed in a main surface region at opposite sides of thegate electrode; and forming a silicon nitride film to cover the gateelectrode, the source and the drain, wherein the silicon nitride film isformed by using a method including: preparing a plasma processingapparatus including a vacuum evacuable processing chamber, a microwavegenerator for generating microwaves, a planar antenna having slots tointroduce the microwaves from the microwave generator into theprocessing chamber through the slots, and a gas supply system forsupplying a source gas for film formation into the processing chamber;loading a substrate to be processed into the processing chamber; andintroducing a nitrogen-containing gas and a silicon-containing gas intothe processing chamber, converting the gases into plasma with themicrowaves, and depositing a silicon nitride film on a surface of thesubstrate by using the plasma, wherein an ammonia gas is used as thenitrogen-containing gas and the silicon nitride film is formed at aprocess pressure of 6.7 Pa or more to have a tensile stress of 400 MPaor more.

In accordance with a fifth aspect of the present invention, there isprovided a method for manufacturing a semiconductor device, comprising:preparing a structure having a gate electrode formed on a main surfaceof a semiconductor substrate through an insulating film, and a sourceand a drain formed in a main surface region at opposite sides of thegate electrode; and forming a silicon nitride film to cover the gateelectrode, the source and the drain, wherein the silicon nitride film isformed by using a method including: preparing a plasma processingapparatus including a vacuum evacuable processing chamber, a microwavegenerator for generating microwaves, a planar antenna having slots tointroduce the microwaves from the microwave generator into theprocessing chamber through the slots, and a gas supply system forsupplying a source gas for film formation into the processing chamber;loading a substrate to be processed into the processing chamber; andintroducing a nitrogen-containing gas and a silicon-containing gas intothe processing chamber, converting the gases into plasma with themicrowaves, and depositing a silicon nitride film on a surface of thesubstrate by using the plasma, wherein a nitrogen gas is used as thenitrogen-containing gas and the silicon nitride film is formed at aprocess pressure less than 5.3 Pa to have a compressive stress of 800MPa or more.

In accordance with a sixth aspect of the present invention, there isprovided a storage medium, which is operated on a computer and stores aprogram for controlling a plasma processing apparatus including a vacuumevacuable processing chamber, a microwave generator for generatingmicrowaves, a planar antenna having slots to introduce the microwavesfrom the microwave generator into the processing chamber through theslots, and a gas supply system for supplying a source gas for filmformation into the processing chamber, wherein the program controls theplasma processing apparatus to perform a plasma CVD method including:loading a substrate to be processed into the processing chamber; andintroducing a nitrogen-containing gas and a silicon-containing gas intothe processing chamber, converting the gases into plasma with themicrowaves, and depositing a silicon nitride film on a surface of thesubstrate by using the plasma, wherein a stress of the silicon nitridefilm is controlled by selecting a type of the nitrogen-containing gasand a process pressure.

In accordance with a seventh aspect of the present invention, there isprovided a plasma processing apparatus comprising: a vacuum evacuableprocessing chamber in which a substrate to be processed is loaded; amicrowave generator for generating microwaves; a planar antenna havingslots to introduce the microwaves from the microwave generator into theprocessing chamber through the slots; a gas supply system for supplyinga source gas for film formation into the processing chamber; and acontroller for controlling the plasma processing apparatus to perform aplasma CVD method including loading a substrate to be processed into theprocessing chamber, introducing a nitrogen-containing gas and asilicon-containing gas into the processing chamber, converting the gasesinto plasma with the microwaves, and depositing a silicon nitride filmon a surface of the substrate by using the plasma, wherein a stress ofthe silicon nitride film is controlled by selecting a type of thenitrogen-containing gas and a process pressure.

In accordance with the plasma CVD method of the present invention, asilicon nitride film having a desired stress can be formed by using aplasma process apparatus in which microwaves are introduced into aprocessing chamber through a planar antenna having slots to generateplasma, and selecting a type of N-containing gas and a process pressure.For instance, when an ammonia gas is used as the N-containing gas andfilm formation is performed at a process pressure of 6.7 Pa or more, thesilicon nitride film may be formed to have a tensile stress of 400 MPaor more. Further, when a nitrogen gas is used as the N-containing gasand film formation is performed at a process pressure less than 5.3 Pa,the silicon nitride film may be formed to have a compressive stress of800 MPa or more.

The plasma process apparatus, in which microwaves are introduced intothe processing chamber through a planar antenna having slots to generateplasma, can perform a process by using plasma having a high density anda low electron temperature. Accordingly, it is possible to surely reduceplasma damage in the plasma CVD. Thus, as the plasma processingapparatus is used, it is possible to extend a selection range of plasmaCVD conditions such as a type of N-containing gas and a process pressureand to precisely control the stress of the silicon nitride film.

As described above, since the plasma CVD method of the present inventioncan not only precisely control the stress of the silicon nitride film,but also suppress plasma damage, it is effective when a silicon nitridefilm having a stress is formed in the manufacture of varioussemiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a cross sectional view of an exemplary plasmaprocessing apparatus for performing a method in accordance with thepresent invention;

FIG. 2 is a plan view showing a planar antenna member of the plasmaprocessing apparatus of FIG. 1;

FIG. 3 schematically shows a cross sectional view of a transistor inwhich a silicon nitride film having a stress is used as a coating film;

FIG. 4A is a cross sectional view showing a step of a method formanufacturing a semiconductor device by using a plasma CVD method inaccordance with an embodiment of the present invention, which shows astate before a silicon nitride film is formed;

FIG. 4B is a cross sectional view showing a step of a method formanufacturing a semiconductor device by using a plasma CVD method inaccordance with an embodiment of the present invention, which shows astate during a plasma CVD process;

FIG. 4C is a cross sectional view showing a step of a method formanufacturing a semiconductor device by using a plasma CVD method inaccordance with an embodiment of the present invention, which shows astate after a silicon nitride film having a stress is formed by plasmaCVD;

FIG. 5 schematically shows a cross sectional view of a CMOS transistorin which a silicon nitride film having a stress is used as a coatingfilm;

FIG. 6 schematically shows a cross sectional view of a nonvolatilememory in which a silicon nitride film having a stress is used as acoating film;

FIG. 7 is a graph showing the relationship between a stress of thesilicon nitride film and a pressure in plasma CVD;

FIG. 8A is a graph showing the relationship between a hydrogenconcentration in the silicon nitride film and a Si₂H₆ flow rate inplasma CVD at a process pressure of 40.0 Pa;

FIG. 8B is a graph showing the relationship between a hydrogenconcentration in the silicon nitride film and a Si₂H₆ flow rate inplasma CVD at a process pressure of 133.3 Pa;

FIG. 8C is a graph showing the relationship between a hydrogenconcentration in the silicon nitride film and a Si₂H₆ flow rate inplasma CVD at a process pressure of 400 Pa;

FIG. 9 is a graph showing the relationship between Si₂H₆/NH₃ and astress applied to the silicon nitride film at a pressure of 666 Pa (5Torr);

FIG. 10 is a graph showing the relationship between a process pressureand a stress of the silicon nitride film while a Si₂H₆ flow rate ischanged to 2 mL/min (sccm), 5 mL/min (sccm) and 10 mL/min (sccm);

FIG. 11 is a graph showing the relationship between a process pressureand an N—H bond concentration at Si₂H₆ flow rates of 2 mL/min (sccm), 5mL/min (sccm) and 10 mL/min (sccm);

FIG. 12 is a graph showing the relationship between a process pressureand a Si—H bond concentration at Si₂H₆ flow rates of 2 mL/min (sccm), 5mL/min (sccm) and 10 mL/min (sccm);

FIG. 13A is a graph showing the relationship among the stress of thesilicon nitride film, the temperature and the gap in plasma CVD in acase of tensile stress;

FIG. 13B is a graph showing the relationship among the stress of thesilicon nitride film, the temperature and the gap in plasma CVD in acase of compressive stress;

FIG. 14 is a Jg map of the silicon nitride film having a tensile stress;

FIG. 15 is a Jg map of the silicon nitride film having a compressivestress;

FIG. 16A is a graph showing the relationship between the stress of thesilicon nitride film and annealing time in a case of tensile stress; and

FIG. 16B is a graph showing the relationship between the stress of thesilicon nitride film and annealing time in a case of compressive stress.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings which form a parthereof. FIG. 1 schematically shows a cross sectional view of a plasmaprocessing apparatus for forming a silicon nitride film in accordancewith the present invention. The plasma processing apparatus 100 isconfigured as a radial line slot antenna (RLSA) microwave plasmaprocessing apparatus capable of generating microwave-excited plasmahaving a high density and a low electron temperature by introducingmicrowaves into a processing chamber with a planar antenna,particularly, RLSA, having a plurality slots. In the plasma processingapparatus 100, a process can be performed by plasma having a plasmadensity of 1×10¹⁰ to 5×10¹²/cm³ and a low electron temperature of 0.7 to2 eV. Thus, the plasma processing apparatus 100 can be usefully usedwhen a silicon nitride film is formed by using a plasma CVD method in amanufacturing process of various semiconductor devices.

The plasma processing apparatus 100 includes an airtightly sealed andapproximately cylindrical chamber 1, which is grounded. Alternatively,the chamber 1 may have a polygonal sectional shape as viewed from above.A circular opening 10 is formed at an approximately central portion of alower wall 1 a of the chamber 1. An exhaust chamber 11 communicatingwith the opening 10 is provided at the lower wall 1 a to be protrudeddownward. The exhaust chamber 11 is connected to an exhaust device 24through an exhaust pipe 23.

A mounting table 2 made of ceramics, such as AlN, having high thermalconductivity is disposed in the chamber 1 to horizontally support asilicon wafer (hereinafter, simply referred to as a “wafer”) W servingas a target substrate. The mounting table 2 is supported by acylindrical supporting member 3 made of ceramics such as AlN andextending upward from a central bottom portion of the exhaust chamber11. The mounting table 2 is provided with a cover ring 4 for covering anouter peripheral portion of the mounting table 2 and guiding the waferW. The cover ring 4 is made of, for example, quartz, AlN, Al₂O₃, SiN,etc.

A resistance heater 5 is embedded in the mounting table 2. The heater 5is supplied with power from a heater power supply 5 a to heat themounting table 2, thereby uniformly heating the wafer W serving as atarget substrate. Further, the mounting table 2 is provided with athermoelectric couple 6 to control a heating temperature of the wafer Wwithin a range from a room temperature to 900° C. Wafer supporting pins(not shown) are provided in the mounting table 2 to be protruded fromthe surface of the mounting table 2 and retracted into the mountingtable, thereby supporting and moving the wafer W up and down.

Annular gas inlets 15 a and 15 b are provided at upper and lower sidesat an upper plate 27 to be described later and a sidewall of the chamber1, respectively. The gas inlets 15 a and 15 b are connected to a gassupply system 16 for supplying a source gas and a plasma excitation gas.Each of the gas inlets 15 a and 15 b may have a nozzle or shower headshape.

The gas supply system 16 includes, for example, a nitrogen-containinggas supply source 17, a silicon-containing gas supply source 18 and anonreactive gas supply source 19. The nitrogen-containing gas supplysource 17 is connected to the gas inlet 15 a provided at the upper side,and both the silicon-containing gas supply source 18 and the nonreactivegas supply source 19 are connected to the gas inlet 15 b provided at thelower side.

The N-containing gas serving as a source gas for film formation mayinclude nitrogen (N₂), ammonia (NH₃), or hydrazine derivatives such asmonomethyl hydrazine (MMH).

The Si-containing gas serving as another source gas for film formationmay include silane (SiH₄), preferably, disilane (Si₂H₆), ortrisilylamine (TSA) [(SiH₃)₃N]. Preferably, disilane (Si₂H₆) is used asthe Si-containing gas.

Further, the nonreactive gas may include, for example, N₂ gas or raregas. The rare gas serving as a plasma excitation gas may include, forexample, Ar, Kr, Xe and He gas. In the present invention, the(tensile/compressive) direction of stress of the silicon nitride filmcan be controlled by selecting the source gas for film formation as willbe described later.

The N-containing gas reaches the gas inlet 15 a through a gas line 20and, then, is introduced into the chamber 1 through the gas inlet 15 a.Further, the Si-containing gas and the nonreactive gas reach the gasinlet 15 b through gas lines 20 and, then, are introduced into thechamber 1 through the gas inlet 15 b. Each of the gas lines 20 connectedto each of the gas supply sources is provided with a mass flowcontroller 21 and valves 22 located at the front and rear of the massflow controller 21 so as to switch the supplied gas or control a flowrate thereof. The rare gas for plasma excitation, for example, Ar, isoptional and may not be supplied simultaneously with the source gas forfilm formation.

The exhaust pipe 23 is connected to the side surface of the exhaustchamber 11. The exhaust pipe 23 is connected to the exhaust device 24including a high-speed vacuum pump. As the exhaust device 24 isoperated, the gas in the chamber 1 uniformly moves to a space 11 a ofthe exhaust chamber 11 along peripheral and lower portions of themounting table 2 and is discharged through the exhaust pipe 23.Accordingly, the inner pressure of the chamber 1 may reach apredetermined vacuum level of, for example, 0.133 Pa at a high speed.

At the sidewall of the chamber 1, there are provided a loading/unloadingport 25 through which the wafer W is delivered between the chamber 1 anda transfer chamber (not shown) adjacent to the plasma processingapparatus 100, and a gate valve 26 for opening and closing theloading/unloading port 25.

The chamber 1 has an upper opening, and the annular upper plate 27 isjoined to the upper opening. An annular support portion 27 a is formedat an inner peripheral lower portion of the upper plate 27 to beprotruded toward a space in the chamber 1. A microwave transmittingplate 28, made of dielectric ceramics such as quartz, Al₂O₃ and AlN totransmit microwaves, is airtightly provided on the support portion 27 athrough a seal member 29. Accordingly, the inside of the chamber 1 ismaintained in a sealed state.

A planar antenna member 31 having a circular plate shape is provided onthe transmitting plate 28 to face the mounting table 2. The planarantenna member may have a rectangular plate shape without being limitedto a circular plate shape. The planar antenna member 31 is fixedlyinstalled at an upper end of the sidewall of the chamber 1. The planarantenna member 31 is formed of a gold or silver plated copper oraluminum plate. The planar antenna member 31 has a plurality ofslot-shaped microwave radiation holes 32 formed through the planarantenna member 31 in a predetermined pattern to radiate microwaves.

As shown in FIG. 2, the microwave radiation holes 32 have pairs of longslots, wherein a pair of the microwave radiation holes 32 are generallyarranged in a “T” shape. The microwave radiation holes 32 are arrangedin a concentric circular pattern. The length and arrangement interval ofthe microwave radiation holes 32 depend on the wavelength (λg) ofmicrowaves within a waveguide 37. For example, the microwave radiationholes 32 may be arranged at intervals of λg/4, λg/2 or λg. In FIG. 2, aninterval between adjacent microwave radiation holes 32 on differentconcentric circles is represented by Ar. Also, the microwave radiationholes 32 may have a circular shape or circular arc shape. No particularlimitation is imposed on the arrangement of the microwave radiationholes 32. For example, the microwave radiation holes 32 may be arrangedin a spiral or radial pattern in addition to the concentric circularpattern.

A wave retardation member 33 having a larger dielectric constant thanthat of a vacuum is provided on the upper surface of the planar antennamember 31. Since microwaves have a longer wavelength in a vacuum, thewave retardation member 33 functions to shorten the wavelength ofmicrowaves to control the plasma. The planar antenna member 31 may be incontact with or separated from the transmitting plate 28 and the waveretardation member 33, but it is preferable that the planar antennamember 31 is in contact with the transmitting plate 28 and the waveretardation member 33, respectively.

A shield lid 34 made of a metal material, for example, aluminum orstainless steel is provided on the upper surface of the chamber 1 tocover the planar antenna member 31 and the wave retardation member 33.The upper surface of the chamber 1 and the shield lid 34 are sealed witha seal member 35. A cooling water path 34 a is formed in the shield lid34 to cool the shield lid 34, the wave retardation member 33, the planarantenna member 31 and the transmitting plate 28 by flowing cooling watertherethrough. Further, the shield lid 34 is grounded.

An opening 36 is formed at an upper central portion of the shield lid 34to be connected to the waveguide 37. A microwave generator 39 forgenerating microwaves is connected to an end portion of the waveguide 37through a matching circuit 38. Accordingly, microwaves having afrequency of, for example, 2.45 GHz generated by the microwave generator39 are propagated through the waveguide 37 to the planar antenna member31. Further, microwaves having a frequency of 8.35 GHz or 1.98 GHz maybe used.

The waveguide 37 includes a coaxial waveguide 37 a having a circularcross section and extending upward from the opening 36 of the shield lid34, and a rectangular waveguide 37 b connected to an upper end of thecoaxial waveguide 37 a through a mode converter 40 and extendinghorizontally. The mode converter 40 provided between the rectangularwaveguide 37 b and the coaxial waveguide 37 a functions to convertmicrowaves propagating in a TE mode through the rectangular waveguide 37b into TEM mode microwaves. An inner conductor 41 is installed at thecenter of the coaxial waveguide 37 a and a lower end portion of theinner conductor 41 is fixedly connected to a central portion of theplanar antenna member 31. Accordingly, the microwaves are efficiently,uniformly and radially propagated to the planar antenna member 31through the inner conductor 41 of the coaxial waveguide 37 a.

Each component of the plasma processing apparatus 100 is connected toand controlled by a process controller 50 having a CPU. A user interface51, including a keyboard for inputting commands or a display fordisplaying an operation status of the plasma processing apparatus 100,is connected to the process controller 50 to allow a process manager tomanage the plasma processing apparatus 100.

Further, the process controller 50 is connected to a storage unit 52which stores recipes including control programs (software) forimplementing various processes in the plasma processing apparatus 100under control of the process controller 50, process condition data andthe like.

If necessary, as a certain recipe is retrieved from the storage unit 52in accordance with an instruction inputted through the user interface 51and transmitted to the process controller 50, a desired process isperformed in the plasma processing apparatus 100 under control of theprocess controller 50. Further, the recipes including control programs,process condition data and the like can be stored in and retrieved froma computer-readable storage medium such as a CD-ROM, a hard disk, aflexible disk and a flash memory, or retrieved through an on-lineconnected via, for example, a dedicated line to another apparatusavailable all the time.

The plasma processing apparatus 100 can not only perform a plasmaprocess without damaging a base film or the like at a low temperature of800° C. or less, but also realize excellent plasma uniformity andprocess uniformity.

In the RLSA type plasma processing apparatus 100, a silicon nitride filmcan be deposited on the surface of the wafer W in the following stepsusing a plasma CVD method.

First, the wafer W is loaded into the chamber 1 through theloading/unloading port 25 by opening the gate valve 26 and mounted onthe mounting table 2. Then, N-containing gas and Si-containing gas areintroduced into the chamber 1 at predetermined flow rates, respectively,through the gas inlets 15 a and 16 b from the N-containing gas supplysource 17 and the Si-containing gas supply source 18 of the gas supplysystem 16.

Next, the microwaves generated from the microwave generator 39 aretransmitted to the waveguide 37 through the matching circuit 38. Afterthe microwaves sequentially pass through the rectangular waveguide 37 b,the mode converter 40, and the coaxial waveguide 37 a, the microwavesare supplied to the planar antenna member 31 through the inner conductor41. Then, the microwaves are radiated into a space above the wafer W inthe chamber 1 through the slots of the planar antenna member 31 and thetransmitting plate 28. The microwaves propagate in a TE mode in therectangular waveguide 37 b and are converted into TEM mode microwaves bythe mode converter 40 to propagate in the coaxial waveguide 37 a towardthe planar antenna member 31. For example, output power of themicrowaves may range from 500 to 3000 W.

An electromagnetic field is formed in the chamber 1 by the microwavesradiated into the chamber 1 from the planar antenna member 31 throughthe transmitting plate 28, thereby converting the N-containing gas andthe Si-containing gas into plasma. The microwave-excited plasma producedby the radiation of the microwaves through the plural holes 32 of theplanar antenna member 31 has a high density of about 1×10¹⁰ to5×10¹²/cm³ and a low electron temperature of about 1.5 eV or less in thevicinity of the wafer W. The microwave-excited plasma causes littleion-induced damage to the base film and has a high density. Accordingly,the source gases are highly dissociated in the plasma to produce activespecies such as SiH, NH, N, and H by high density plasma. The activespecies react with each other to deposit a thin film of silicon nitrideSixNy (x and y are not necessarily determined based on stoichiometry andhave different values according to conditions).

In the present invention, the direction and strength of stress of thesilicon nitride film can be controlled by selecting film formationconditions in a plasma CVD method. Specifically, for example, when atensile stress is applied to the silicon nitride film during formationthereof, it is preferable to use a NH₃ gas as the N-containing gas and aSi₂H₆ gas as the silicon-containing gas. In this case, a flow rate ofNH₃ gas is set at 100 to 3000 mL/min (sccm), preferably, 400 to 1000mL/min (sccm), and a flow rate of Si₂H₆ gas is set at 1 to 30 mL/min(sccm), preferably, 5 to 20 mL/min (sccm).

When the Si₂H₆ gas and NH₃ gas are used, a silicon nitride film having ahigh tensile stress can be formed by setting a process pressure to beslightly high in the plasma CVD. For example, in order to form a siliconnitride film having a tensile stress of 400 MPa or more by using Si₂H₆gas and NH₃ gas, it is preferable to set a process pressure at 6.7 Pa(50 mTorr) or more. Further, in order to form a silicon nitride filmhaving a high tensile stress of 800 MPa or more, for example, 800 to2000 MPa, it is preferable to set a process pressure at 40 Pa or more,for example, 40 to 266.6 Pa (300 mTorr to 2 Torr). Further, in order toform a silicon nitride film having a high tensile stress of 1000 MPa ormore, for example, 1000 to 2000 MPa, it is preferable to set a processpressure at 53.3 Pa or more, for example, 53.3 to 266.6 Pa (400 mTorr to2 Torr). Further, in order to form a silicon nitride film having a hightensile stress of 1500 MPa or more, for example, 1500 to 2000 MPa, it ispreferable to set a process pressure at 133.3 Pa or more, for example,133.3 to 266.6 Pa (1 Torr to 2 Torr).

When a process pressure is kept constant, as a process temperature ofplasma CVD becomes higher, the tensile stress of the silicon nitridefilm tends to be stronger. Accordingly, it is preferable to heat themounting table 2 to 300 to 800° C. Further, since a film can be formedat a low temperature in the plasma CVD method, it is more preferable toheat the mounting table 2 to 300 to 450° C. in a viewpoint of themanufacture of devices.

Further, as a gap G (distance from the bottom surface of thetransmitting plate 28 to the upper surface of the mounting table 2) inthe plasma processing apparatus 100 becomes larger, the tensile stressof the silicon nitride film tends to be stronger. Accordingly, it ispreferable to set the gap G to be, for example, about 100 to 300 mm.

When a compressive stress is applied to a silicon nitride film duringformation thereof, it is preferable to use a N₂ gas as the N-containinggas and a Si₂H₆ gas as the Si-containing gas. In this case, a flow rateof N₂ gas is set at 100 to 3000 mL/min (sccm), preferably, 800 to 2000mL/min (sccm), and a flow rate of Si₂H₆ gas is set at 1 to 30 mL/min(sccm), preferably, 1 to 10 mL/min (sccm).

When the Si₂H₆ gas and N₂ gas are used, a silicon nitride film having ahigh compressive stress can be formed by setting a process pressure tobe slightly low in the plasma CVD. For example, in order to form asilicon nitride film having a compressive stress of, for example, 800MPa or more by using Si₂H₆ gas and N₂ gas, it is preferable to set aprocess pressure less than 5.3 Pa (40 mTorr), for example, 1.3 to 5.3 Pa(10 mTorr to 40 mTorr). Further, in order to form a silicon nitride filmhaving a high compressive stress of 1000 MPa or more, for example, 1000to 2000 MPa, it is preferable to set a process pressure at 4 Pa or less,for example, 1.3 to 4 Pa (10 mTorr to 30 mTorr).

When a process pressure is kept constant, as a process temperature ofplasma CVD becomes higher, the compressive stress of the silicon nitridefilm tends to be stronger. Accordingly, it is preferable to heat themounting table 2 to 300 to 800° C., more preferably, 300 to 450° C. in aviewpoint of the manufacture of devices.

Further, as the gap G (distance from the bottom surface of thetransmitting plate 28 to the upper surface of the mounting table 2) inthe plasma processing apparatus 100 becomes larger, the compressivestress of the silicon nitride film tends to be stronger. Accordingly, itis preferable to set the gap G to be, for example, about 100 to 300 mm.

As explained above, as the film formation is performed by using theplasma processing apparatus 100 and selecting the plasma CVD conditions,it is possible to precisely control the (tensile/compressive) directionand magnitude of stress of the silicon nitride film.

Next, an application example of the silicon nitride film formed by usingthe plasma processing apparatus 100 and the plasma CVD method will bedescribed with reference to FIGS. 3 and 4A to 4C. FIG. 3 schematicallyshows a cross sectional view of a metal-oxide-silicon (MOS) transistor200. The MOS transistor 200 includes a gate electrode 103 formed on aP-type or N-type Si layer 101 via a gate insulating film 102 and madeof, for example, polysilicon. A source 104 and a drain 105 are formed atboth side regions of the gate electrode 103, and a channel region 106(portion designated by net-shaped lines in FIG. 3) is formed between thesource 104 and the drain 105. Further, an insulating coating film(liner) 107 having a high stress is formed to cover the gate electrode103. In this application example, the coating film 107 may be formed byusing the plasma processing apparatus 100 and the plasma CVD method. Asdescribed above, the coating film 107 may have a tensile or compressivestress by controlling the plasma CVD conditions.

For instance, when a silicon nitride film having a tensile stress isused as the coating film 107, a stress is applied to the coating film(insulating film) 107 in directions represented by black arrows 108 ofFIG. 3. Further, a stress is applied to silicon of the source 104 andthe drain 105 in contact with the coating film (insulating film) 107 inthe same directions as the black arrows 108. Hence, a stress is alsoapplied to the channel region 106 in the same directions as the blackarrows 108, thereby causing a tensile distortion in the channel region106.

On the other hand, when the coating film 107 has a compressive stress, astress is applied to the coating film (insulating film) 107 indirections represented by white arrows 109 of FIG. 3. Further, a stressis applied to silicon of the source 104 and the drain 105 in contactwith the coating film (insulating film) 107 in the same directions asthe white arrows 109. Hence, a stress is also applied to the channelregion 106 in the same directions as the white arrows 109, therebycausing a compressive distortion in the channel region 106.

When the transistor 200 is an NMOS transistor which uses electrons ascarriers, a tensile distortion applied to the channel region 106increases mobility, whereas a compressive distortion applied to thechannel region 106 decreases mobility. On the other hand, when thetransistor 200 is a PMOS transistor which uses holes as carriers, acompressive distortion applied to the channel region 106 increasesmobility, whereas a tensile distortion applied to the channel region 106decreases mobility.

Hence, when the transistor 200 is an NMOS transistor, saturation drivecurrent or linear drive current can be increased by employing a siliconnitride film having a tensile stress as the coating film (insulatingfilm) 107 and applying a tensile distortion to the channel region 106.Further, when the transistor 200 is a PMOS transistor, saturation drivecurrent or linear drive current can be increased by employing a siliconnitride film having a compressive stress as the coating film (insulatingfilm) 107 and applying a compressive distortion to the channel region106. As described above, the driving performance of the transistor 200can be improved by using a silicon nitride film having a tensile orcompressive stress as the coating film (insulating film) 107. As aresult, it is possible to improve the performance of a semiconductordevice including the transistor 200.

Although the silicon nitride film having a stress is only used as thecoating film (insulating film) 107 in FIG. 3, the silicon nitride filmhaving a stress may be also used as, for example, sidewalls formed atopposite sides of the gate electrode 103.

For example, the transistor 200 may be manufactured by forming thecoating film (insulating film) 107 of a silicon nitride film to coverthe gate electrode 103, the source 104 and the drain 105 of thestructure under conditions capable of applying a tensile or compressivestress thereto by using the plasma processing apparatus 100. FIGS. 4A to4C illustrate cross sectional views showing the steps of a process formanufacturing the transistor 200 by using a plasma nitriding method inaccordance with the present invention.

A transistor structure shown in FIG. 4A may be formed as follows. First,a well (not shown) is formed in the P-type or N-type Si layer 101, and adevice isolation layer is formed by, for example, a LOCOS method orshallow trench isolation (STI) method. Then, the gate insulating film102 of a silicon nitride film, silicon oxide film or the like is formedon the surface of the Si layer 101 by a plasma processing method or heattreatment method. After a polysilicon layer is formed on the gateinsulation layer 102 by using, for example, a CVD method, thepolysilicon layer is etched through a mask pattern formed by using aphotolithography technique to form the gate electrode 103. The structureof the gate electrode is not limited to a single layer structure of thepolysilicon layer. That is, the gate electrode may have a stackstructure including, for example, tungsten, molybdenum, tantalum,titanium, and silicide, nitride and an alloy thereof in order todecrease the resistivity of the gate electrode and to achieve a highspeed transistor. As described above, after the gate electrode 103 isformed, ion implantation and activation are performed to form the source104 and the drain 105.

Then, as shown in FIG. 4B, a silicon nitride film having a tensile orcompressive stress is formed by using the plasma processing apparatus100 to cover the surface of the Si layer 101 and the gate electrode 103.Then, an unnecessary portion of the silicon nitride film is removedbased on a mask pattern formed by a photolithography technique to formthe coating film (insulating film) 107, thereby manufacturing the MOStransistor 200 as shown in FIG. 4C. If necessary, an annealing processmay be performed on the coating film (insulating film) 107.

Further, when a CMOS transistor 300 shown in FIG. 5 is manufactured,film formation, patterning using photolithography, and etching aresequentially performed to form an NMOS region 201 and a PMOS region 202.Further, coating films (insulating films) 203 and 204 may be formed inthe NMOS region 201 and the PMOS region 202, respectively, by formingsilicon nitride films under conditions capable of applying a tensile orcompressive stress thereto in accordance with the present invention andetching the silicon nitride films.

Specifically, a p-type well 211 and an n-type well 212 for forming theNMOS region 201 and the PMOS region 202 are formed in a siliconsubstrate 210, respectively. A poly-Si gate electrode 214 is formed on amain surface of the p-type well 211 through a gate insulating film 213.A source 215 and a drain 216 are formed at both side regions of the gateelectrode 214. Then, sidewalls 217 are formed on both sides of the gateelectrode 214. Meanwhile, a poly-Si gate electrode 224 is formed on amain surface of the n-type well 212 through a gate insulating film 213.A source 225 and a drain 226 are formed at both side regions of the gateelectrode 224. Then, sidewalls 227 are formed on both sides of the gateelectrode 224. Further, a reference numeral 230 designates a deviceisolation region. In this case, the steps are performed as described inFIGS. 4A to 4C.

After the NMOS region 201 and the PMOS region 202 are formed, thesilicon nitride film having a tensile stress is deposited on an entiresurface of the structure by using the plasma processing apparatus 100.The silicon nitride film having a tensile stress in the PMOS region 202is removed by etching to remain the coating film (insulating film) 203of the silicon nitride film having a tensile stress only in the NMOSregion 201.

Thereafter, a silicon nitride film having a compressive stress isdeposited on the wafer W by using the plasma processing apparatus 100.Then, the silicon nitride film having a compressive stress in the NMOSregion 201 is removed by etching to remain the coating film (insulatingfilm) 204 of the silicon nitride film having a compressive stress onlyin the PMOS region 202. Consequently, a CMOS transistor having animproved performance can be manufactured by using the stresses of thesilicon nitride films to cause a tensile distortion in a channel region218 of the NMOS region 201 and a compressive distortion in a channelregion 228 of the PMOS region 202.

Further, the silicon nitride film formed by using the plasma processingapparatus 100 and the plasma CVD may be also applied to a nonvolatilememory 400 shown in FIG. 6. In the nonvolatile memory 400, a tunneloxide film 302 is formed on a main surface of a Si substrate 301, and afloating gate (FG) 304 made of polysilicon is formed thereon. Adielectric film 305 having, for example, an oxide-nitride-oxide (ONO)structure is formed on the floating gate 304. Further, a control gate(CG) 306 made of polysilicon is formed on the dielectric film 305. Aninsulating layer 307 is formed on the control gate 306. Then, anoxidation treatment is performed to form a sidewall oxide film 308 atsidewalls of both the floating gate 304 and the control gate 306. Asource 309 and a drain 310 are formed at both side regions of thefloating gate 304 formed on the main surface of the Si substrate 301. Acoating film (insulating film) 311 of a silicon nitride film having astress is formed to cover the floating gate 304, the control gate 306,the source 309 and the drain 310.

As described above, a distortion can be appropriately applied to thefloating gate 304 by forming a silicon nitride film having a stress asthe coating film (insulating film) 311. In the nonvolatile memory 400,charges of the floating gate 304 may be lost by tunneling into the Sisubstrate to cause tunneling current after passing through the tunneloxide film, thereby causing loss of memory. However, average electronmass and a width of a SiO₂ barrier of the tunnel oxide film 302 mayincrease to reduce the tunneling current by appropriately applying adistortion to the floating gate 304. Thus, the floating gate 304 canstably maintain charges.

Next, an explanation is given of the experimental results which providea basis for the present invention.

First, silicon nitride films were formed under various conditions byusing the plasma processing apparatus 100 and the stress of each siliconnitride film was measured. FIG. 7 is a graph showing a relationshipbetween a process pressure and a stress of the silicon nitride film inthe plasma CVD. A vertical axis of the graph shown in FIG. 7 representsa stress of the silicon nitride film, wherein a positive (plus) valuerepresents a tensile stress and a negative (minus) value represents acompressive stress (in the same way in FIGS. 9, 10, 13A, 13B, 16A and16B). Further, a horizontal axis of the graph shown in FIG. 7 representsa process pressure (mTorr) in log scale, wherein pressure values (mTorr)in an upper line are converted into pressure values (Pa) in a lower line(in the same way in FIGS. 10, 11 and 12).

In the experiment, silicon nitride films having a tensile stress wereformed under the following plasma CVD conditions.

<Conditions for Plasma CVD Film Formation (NH₃/Si₂H₆ Gas Atmosphere)>

NH₃ gas flow rate: 500 mL/min (sccm)

Si₂H₆ gas flow rate: 5 mL/min (sccm)

Process pressure: 2.7 Pa (20 mTorr), 6.7 Pa (50 mTorr), 40.0 Pa (300mTorr) and 133.3 Pa (1 Torr)

Temperature of mounting table 2: 400° C.

Microwave power: 2000 W

Further, silicon nitride films having a compressive stress were formedunder the following plasma CVD conditions.

<Conditions for Plasma CVD Film Formation (N₂/Si₂H₆ Gas Atmosphere)>

N₂ gas flow rate (gas inlet 15 a): 1100 mL/min (sccm)

Si₂H₆ gas flow rate: 1 mL/min (sccm)

N₂ gas flow rate (gas inlet 15 b): 100 mL/min (sccm)

Process pressure: 4.0 Pa (30 mTorr), 6.7 Pa (50 mTorr), 13.3 Pa (100mTorr) and 66.6 Pa (500 mTorr)

Temperature of mounting table 2: 500° C.

Microwave power: 3000 W

When film formation is performed under an NH₃/Si₂H₆ gas atmosphere, asis apparent from the graph of FIG. 7, a tensile stress occurs in eachsilicon nitride film and tends to increase as the process pressureincreases. A tensile stress of about 400 MPa was obtained at a processpressure of about 6.7 Pa. Hence, when a tensile stress is applied to thesilicon nitride film, the process pressure is preferably set to be 6.7Pa (50 mTorr) or more. Further, in order to form a silicon nitride filmhaving a high tensile stress of 800 MPa or more, for example, 800 to2000 MPa, it is preferable to set a process pressure to be 40 MPa ormore, for example, 40 to 266.6 Pa (300 mTorr to 2 Torr). Further, inorder to form a silicon nitride film having a high tensile stress of1000 MPa or more, for example, 1000 to 2000 MPa, it is preferable to seta process pressure to be 53.3 Pa or more, for example, 53.3 to 266.6 Pa(400 mTorr to 2 Torr). Further, in order to form a silicon nitride filmhaving a high tensile stress of 1500 MPa or more, for example, 1500 to2000 MPa, it is preferable to set a process pressure to be 133.3 Pa ormore, for example, 133.3 to 266.6 Pa (1 Torr to 2 Torr).

Further, when film formation is performed under an N₂/Si₂H₆ gasatmosphere, a compressive stress occurs in each silicon nitride film andtends to increase as the process pressure decreases. A compressivestress larger than about 800 MPa was obtained at a process pressure lessthan about 5.3 Pa (40 mTorr). Accordingly, when a compressive stress isapplied to the silicon nitride film, the process pressure is preferablyset to be smaller than 5.3 Pa (40 mTorr). Further, in order to form asilicon nitride film having a high compressive stress of 1000 MPa ormore, for example, 1000 to 1500 MPa, it is preferable to set a processpressure to be 4 Pa or less, for example, 1.3 to 4 Pa (10 mTorr to 30mTorr).

It could be seen from FIG. 7 that the direction and strength of thestress can be precisely controlled by adjusting gas species and aprocess pressure in the plasma CVD.

Next, silicon nitride films were formed by using the plasma processingapparatus 100 while a Si₂H₆ flow rate is changed, and hydrogenconcentrations (Si—H and N—H concentrations) of the silicon nitridefilms were measured. FIGS. 8A to 8C are graphs showing the relationshipbetween Si₂H₆ flow rates and hydrogen concentrations (Si—H concentrationand N—H concentration) in the silicon nitride films. The processpressure of the plasma CVD was set to be 40.0 Pa (300 mTorr) in FIG. 8A,133.3 Pa (1 Torr) in FIG. 8B, and 400 Pa (3 Torr) in FIG. 8C. Further, anitrogen-containing gas, i.e., NH₃ gas, was supplied at a flow rate of500 mL/min (sccm) while a process temperature was set to be 500° C.;microwave power, 2 kW; and a gap G, 155 mm. In the graphs of FIGS. 8A to8C, “Total-H” represents a sum of Si—H and N—H concentrations in thesilicon nitride films.

From the comparison of FIGS. 8A to 8C, it was recognized that the effectof change in Si₂H₆ flow rate on hydrogen concentration was clearer at aprocess pressure of 40.0 Pa (300 mTorr) than at 133.3 Pa (1 Torr) or 400Pa (3 Torr). The silicon nitride film formed by the plasma CVD tends tohave a tensile stress as the hydrogen concentration in the siliconnitride film increases, and the tensile stress tends to be weakened asthe hydrogen concentration decreases. Accordingly, when the processpressure is 40.0 Pa (300 mTorr), the tensile stress can be finelycontrolled by adjusting the Si₂H₆ flow rate.

Next, silicon nitride films were formed in an NH₃/Si₂H₆ gas atmosphereby using the plasma processing apparatus 100 while a Si₂H₆ gas flow rateand a process pressure are changed, and the stress of each siliconnitride film was measured. In this case, flow rates of NH₃ and Ar gaseswere constantly maintained at 400 mL/min (sccm) and 200 mL/min (sccm),respectively. Further, the Si₂H₆ gas flow rate was changed to 2 mL/min(sccm), 5 mL/min (sccm), and 10 mL/min (sccm) and the process pressurewas changed within a range of 9.33 to 1333 Pa (70 to 10000 mTorr).Further, a process temperature was set at 400° C., and microwave powerwas set at 2 kW.

FIG. 9 is a graph showing the relationship between Si₂H₆/NH₃ and thestress applied to the silicon nitride films at a pressure of 666 Pa (5Torr). It can be seen from the graph of FIG. 9 that the tensile stressincreases as Si₂H₆/NH₃ decreases from 0.01 to 0. Accordingly, it wasconcluded that Si₂H₆/NH₃ is preferably set to be 0.01 or less when it isintended to apply a high tensile stress to the silicon nitride film at arelatively high pressure of 666 Pa (5 Torr).

FIG. 10 is a graph showing the relationship between a process pressureand a tensile stress of the silicon nitride film while a Si₂H₆ flow rateis changed to 2 mL/min (sccm), 5 mL/min (sccm) and 10 mL/min (sccm),wherein a horizontal axis and a vertical axis of the graph represent aprocess pressure and a stress of the silicon nitride film, respectively.As is apparent from the graph, the tensile stress of the silicon nitridefilm increases as the process pressure increases to 133.3 Pa (1 Torr)regardless of a Si₂H₆ flow rate. However, when the flow rate of Si₂H₆ is5 mL/min (sccm) or 10 mL/min (sccm), the tensile stress hardly increasesat a process pressure exceeding 133.3 Pa (1 Torr), and decreases at aprocess pressure exceeding 266.6 Pa (2 Torr). On the other hand, whenthe flow rate of Si₂H₆ is 2 mL/min (sccm), the tensile stresscontinuously increases to 1333 Pa (10 Torr).

FIG. 11 is a graph showing the relationship between a process pressureand an N—H bond concentration at Si₂H₆ flow rates of 2 mL/min (sccm), 5mL/min (sccm) and 10 mL/min (sccm), wherein a horizontal axis and avertical axis of the graph represent a process pressure and an N—H bondconcentration, respectively. FIG. 12 is a graph showing the relationshipbetween a process pressure and a Si—H bond concentration at Si₂H₆ flowrates of 2 mL/min (sccm), 5 mL/min (sccm) and 10 mL/min (sccm), whereina horizontal axis and a vertical axis of the graph represent a processpressure and a Si—H bond concentration, respectively. Referring to thesefigures and FIG. 10, when the flow rate of Si₂H₆ is 5 mL/min (sccm) or10 mL/min (sccm), a high tensile stress occurs at a high N—H bondconcentration and a Si—H bond concentration of approximately zero. Inthis case, a tensile stress decreases as an N—H bond concentrationdecreases and a Si—H bond concentration increases. That is, when NH₃ isexcessively supplied, N—H bonds in the film increase under reaction ratecontrol so that the tensile stress increases. On the other hand, whenSi₂H₆ is excessively supplied, Si—H bonds increase under supply ratecontrol so that the tensile stress decreases. Thus, when the flow rateof Si₂H₆ is lowered to 2 mL/min (sccm), a Si—H bond concentration doesnot increase and an N—H bond concentration is maintained even at aprocess pressure of 266 Pa (2 Torr) or more, so that the tensile stressincreases to about 1333 Pa (10 Torr).

Next, silicon nitride films were formed under various conditions byusing the plasma processing apparatus 100, and the relationship amongthe temperature of the mounting table 2, the gap G and the stress wasinvestigated. FIGS. 13A and 13B are graphs showing the relationshipbetween the temperature of the mounting table and the stress at eachgap, wherein tensile stress and compressive stress are shown in FIGS.13A and 13B, respectively. In this experiment, the relationship betweenthe temperature of the mounting table and the stress was investigated ateach gap G of 125 mm, 150 min and 180 on. In this case, a NH₃ gas flowrate was set to be 500 mL/min (sccm); a Si₂H₆ gas flow rate, 5 mL/min(sccm); a process pressure, 133.3 Pa; and microwave power, 2 kW. It canbe seen from the graphs of FIGS. 13A and 13B that both the tensilestress and the compressive stress tend to increase as the temperature ofthe mounting table 2 increases. Also, it can be seen that both thetensile stress and the compressive stress tend to increase as the gap Gincreases.

Thus, a high temperature is preferable in order to increase a stresswhether a tensile or compressive stress is applied to the siliconnitride film. However, a low temperature is preferable in a viewpoint ofthe manufacture of devices. Also, one of advantages of plasma CVD isthat film formation can be achieved at a low temperature. Inconsideration of these facts, it is preferable that the mounting table 2is heated to a temperature of 300 to 450° C. Further, it is preferablethat the gap G is set to be, for example, 100 to 300 mm.

Hereinafter, an explanation is given of test results showing effects ofthe present invention.

(1) Charge-up Damage Evaluation

A wafer (a diameter of 200 mm) including a plurality of MOS capacitorswas used for the test. The test wafer includes 1 to 96 chips, each chiphaving six types of MOS capacitors in which antenna ratios AAR (arearatios of polysilicon electrodes and gate insulating films of the MOScapacitors) are 10, 100, 1,000, 10,000, 100,000 and 1,000,000. After asilicon nitride film was formed on a surface of the test wafer by usingthe plasma processing apparatus 100, damage of the MOS capacitors wasevaluated by leakage current obtained from the current-voltagecharacteristics of the MOS capacitors. In this test, failure (charge-updamage) was determined when Jg exceeds 1×10⁻⁹ [A/μm²] at −4.375 V (−12.5MV/cm).

A silicon nitride film having a tensile stress was formed by using theplasma processing apparatus 100 of FIG. 1 under the plasma CVDconditions in which a NH₃ gas flow rate is set to be 500 mL/min (sccm);a Si₂H₆ gas flow rate, 5 mL/min (sccm); a process pressure, 133.3 Pa (1Torr); a temperature of the mounting table 2, 500° C.; microwave power,2000 W; and the gap, 180 mm. The silicon nitride film was formed to havea tensile stress of about 1500 MPa.

A silicon nitride film having a compressive stress was formed by usingthe plasma processing apparatus 100 of FIG. 1 under the plasma CVDconditions in which a N₂ gas flow rate supplied through the gas inlet 15a is set to be 1100 mL/min (sccm); a N₂ gas flow rate and a Si₂H₆ gasflow rate supplied through the gas inlet 15 b, 100 mL/min (sccm) and 1mL/min (sccm), respectively; a process pressure, 2.66 Pa (20 mTorr); atemperature of the mounting table 2, 500° C.; microwave power, 3000 W;and the gap, 180 mm. The silicon nitride film was formed to have acompressive stress of about 1000 MPa.

Both the films having tensile and compressive stresses were formed tohave a thickness of 20 mm.

FIG. 14 is a Jg map showing charge-up damage when a silicon nitride filmhaving a tensile stress is formed on the test wafer. FIG. 15 is a Jg mapshowing charge-up damage when a silicon nitride film having acompressive stress is formed on the test wafer. FIGS. 14 and 15 aremeasurement results in the MOS capacitors having an AAR of 1,000,000.

As shown in FIGS. 14 and 15, the Jg value is sufficiently smaller than1×10⁻⁹[A/μm²] even at an AAR of 1,000,000 at which leakage easilyoccurs. Although not shown in the drawings, the Jg values were farsmaller at other AARs. As described above, it was checked that plasmadamage hardly occurs when a silicon nitride film having a stress isformed by using the plasma processing apparatus 100.

(2) Step Coverage Evaluation

A silicon nitride film having a tensile stress was formed on a test Sisubstrate having a trench by using the plasma processing apparatus 100under plasma CVD conditions in which a NH₃ gas flow rate is set to be500 mL/min (sccm); a Si₂H₆ gas flow rate, 5 mL/min (sccm); a processpressure, 133.3 Pa (1 Torr); a temperature of the mounting table 2, 500°C.; and microwave power, 2000 W. The trench has an aspect ratio(depth/width) of 1/1.

Film thicknesses of a top portion (flat portion around the trench), aside portion (sidewall of the trench) and a bottom portion (bottomportion of the trench) of the silicon nitride film were measured toevaluate step coverage. A film thickness ratio of the side portion tothe top portion (film thickness of the side portion/film thickness ofthe top portion×100) is 91%, and a film thickness ratio of the bottomportion to the top portion (film thickness of the bottom portion/filmthickness of the top portion×100) is 97%, thereby obtaining good stepcoverage.

(3) Thermal Resistance Evaluation

Silicon nitride films having tensile and compressive stresses wereformed by using the plasma processing apparatus 100 and annealed toinvestigate an effect of heat treatment on the stresses of the siliconnitride films. The film formation and annealing conditions are asfollows.

<Plasma CVD Conditions (NH₃/Si₂H₆ Gas Atmosphere)>

NH₃ gas flow rate: 400 mL/min (sccm)

Si₂H₆ gas flow rate: 5 mL/min (sccm)

Process pressure: 133.3 Pa (1000 mTorr)

Temperature of mounting table 2: 500° C.

Microwave power: 2000 W

<Plasma CVD Conditions (N₂/Si₂H₆ Gas Atmosphere)>

N₂ gas flow rate (gas inlet 15 a): 1100 mL/min (sccm)

Si₂H₆ gas flow rate: 1 mL/min (sccm)

N₂ gas flow rate (gas inlet 15 b): 100 mL/min (sccm)

Process pressure: 2.6 Pa (20 mTorr)

Temperature of mounting table 2: 500° C.

Microwave power: 1000 W

<Annealing Conditions>

Process temperature: 800° C.

Process pressure: 101308 Pa (760 Torr)

Process time: 0 minutes (unprocessed), 10 minutes or 20 minutes

FIGS. 16A and 16B are graphs showing the relationships between thestresses of the silicon nitride films and annealing time periods,wherein FIG. 16A shows a case of tensile stress and FIG. 16B shows acase of compressive stress. It can be seen from FIGS. 16A and 16B thatthe silicon nitride film having a tensile or compressive stress, formedunder the above-described conditions by using Si₂H₆ and N₂ or NH₃ gasesas source gases, exhibits very small variations in stress before andafter annealing and has excellent thermal resistance. As a result, itwas concluded that the silicon nitride film formed by using Si₂H₆ and N₂or NH₃ gases as source gases has excellent thermal resistance in heattreatments repeated in the manufacture of various semiconductor devices.

The present invention is not limited to the above-described embodimentsand various changes and modifications may be made without departing fromthe scope of the invention.

For instance, although the silicon nitride film having a high tensile orcompressive stress is used as a coating film of the transistor so as toimprove driving characteristics of the transistor, the present inventionmay be applied to the manufacture of various semiconductor devicescapable of improving device characteristics by use of the stress withoutbeing limited thereto.

What is claimed is:
 1. A method for forming a silicon nitride filmhaving a high stress by using a plasma CVD method, comprising: loading asubstrate to be processed in a processing chamber; introducing anitrogen gas and a silicon-containing gas into the processing chamber;introducing microwaves into the processing chamber through a planarantenna having slots to generate a plasma of the nitrogen gas and thesilicon-containing gas; and forming a silicon nitride film having a highcompressive stress on the substrate by using the plasma CVD method,wherein the silicon nitride film is formed to have a compressive stresslarger than 800 MPa at a process pressure of 1.3 Pa to 5.3 Pa and aprocess temperature of 300° C. to 800° C. in the processing chamber,wherein the strength of the compressive stress is controlled by changingthe process pressure, wherein active nitrogen species in the plasma areoriginated only from the nitrogen gas, and wherein the high compressivestress of the silicon nitride film is maintained without a substantialchange even when the silicon nitride film is annealed.
 2. The method ofclaim 1, wherein silicon nitride film is formed at a process pressure of1.3 Pa to 4 Pa to have a compressive stress of 1000 MPa or more.
 3. Themethod of claim 1, wherein the silicon-containing gas is disilane(Si₂H₆).
 4. A method of manufacturing a CMOS transistor, comprising thefilm forming method of claim
 1. 5. The method of claim 1, wherein thehigh compressive stress of the silicon nitride film is maintained within200 MPa of the 800 MPa even when the silicon nitride film is annealed.6. A method for forming a silicon nitride film having a high stress byusing a plasma CVD method, comprising: loading a substrate to beprocessed in a processing chamber; introducing an ammonia gas and asilicon-containing gas into the processing chamber; generating a plasmaof the ammonia gas and the silicon-containing gas; and forming a siliconnitride film having a high tensile stress on the substrate by using theplasma CVD method, wherein the silicon nitride film is formed to have atensile stress of 400 MPa or more at a process pressure of 6.7 Pa ormore and a process temperature of 300° C. to 800° C. in the processingchamber, wherein the strength of the tensile stress is controlled bychanging the process pressure, wherein active nitrogen species in theplasma are originated only from the ammonia gas, and wherein the hightensile stress of the silicon nitride film is maintained without asubstantial change even when the silicon nitride film is annealed. 7.The method of claim 6, wherein the silicon nitride film is formed at aprocess pressure of 40 Pa to 266.6 Pa to have a tensile stress of 800MPa to 2000 MPa.
 8. The method of claim 6, wherein the silicon nitridefilm is formed at a process pressure of 133.3 Pa to 266.6 Pa to have atensile stress of 1500 MPa to 2000 MPa.
 9. The method of claim 6,wherein the silicon-containing gas is disilane (Si₂H₆).
 10. A method ofmanufacturing a CMOS transistor, comprising the film forming method ofclaim
 6. 11. The method of claim 6, wherein the high tensile stress ofthe silicon nitride film is maintained within 100 MPa of the 400 MPaeven when the silicon nitride film is annealed.
 12. A plasma CVDapparatus for forming a silicon nitride film having a high stress,comprising: a processing chamber in which a substrate to be processed isloaded; a gas supply system for supplying a nitrogen gas and asilicon-containing gas into the processing chamber; a plasma generatingunit for generating a plasma of the nitrogen gas and thesilicon-containing gas in the processing chamber; a gas exhaust unit forexhausting an inside of the processing chamber; and a controller forcontrolling the plasma CVD apparatus to form the silicon nitride filmhaving a compressive stress larger than 800 MPa on the substrate byusing a plasma CVD method by introducing the nitrogen gas and thesilicon-containing gas from the gas supply system into the processingchamber and generating a plasma of the nitrogen gas and thesilicon-containing gas in the processing chamber by the plasmagenerating unit at a process pressure smaller than 5.3 Pa and a processtemperature of 300° C. to 800° C. in the processing chamber, wherein thestrength of the compressive stress is controlled by changing the processpressure, wherein active nitrogen species in the plasma are originatedonly from the nitrogen gas, and wherein the compressive stress of thesilicon nitride film is maintained without a substantial change evenwhen the silicon nitride film is annealed.
 13. The method of claim 9,wherein a flow rate ratio of Si₂H₆/NH₃ is 0.01 or less.
 14. Theapparatus of claim 12, wherein the compressive stress of the siliconnitride film is maintained within 200 MPa of the 800 MPa even when thesilicon nitride film is annealed.